Systemic lupus erythematosus (SLE or lupus) is an important chronic disease in young women and it has served as a prototype for studying the interrelationships between immunologic diseases in the mother and fetal development. Pregnancy superimposed on lupus may alter the course of the illness. Conversely, the underlying disease may affect the natural history of pregnancy. The reasons for such changes in maternal SLE disease activity during pregnancy have not been clearly defined. Excessive fetal morbidity and mortality have been reported in women with SLE, but only some of the adverse fetal outcomes have been explained. The two research questions to be addressed in the study are: (1) Is pregnancy an independent risk factor affecting disease activity in women with SLE? and (2) Is maternal SLE disease activity a risk factor affecting pregnancy outcome? These questions will be answered in this prospective case-control study of women with SLE in the 100-mile Pittsburgh Metropolitan referral area. A lupus registry consisting of women of childbearing age with SLE will be formed. A patient is defined as a case if she becomes pregnant. Medical, obstetrical, and exposure histories are obtained, disease activity is measured by a validated instrument, and a blood sample is drawn at three month intervals from the time the pregnancy is confirmed until the woman is six months postpartum. Infants will be examined at birth and at six months of age for growth parameters and morphologic abnormalities. Six registry patients not currently pregnant will be randomly chosen each month to be followed as controls. The controls will be followed at three month intervals for 15 months with the same measurements, excluding pregnancy specific questions, obtained as the cases. Comparison between cases and controls of baseline and longitudinal data will be performed to assess pregnancy as an independent risk factor for change in disease activity. A subset analysis will be performed on the cases to determine risk factors such as disease activity or exposures and their effect on pregnancy outcome. This case-control study can serve as a model for understanding changes in maternal disease and adverse pregnancy outcomes in other chronic diseases.